The present invention relates to a wet type image developing device for use in an electrophotographic printer.
In a conventional electrophotographic printer, because of the utilization of a photo-conductivities, an electrostatic latent image is formed in accordance with an image information on a photosensitive member such as a photosensitive drum. The latent image is visualized by the adhesion of a coloring particles such as toners, and the toner image undergoes development. Here, known is a dry type developing method in which dry toner powders are used. Also known is a wet type developing method in which the toner powders are dispersed in an insulative liquid. In the latter method, dipping method, dripping method, injection method and contact method are available for forming the toners onto the photosensitive member.
According to a conventional contact type method in the wet type image developing mode, a developing roller formed of a sponge is used. During rotation of the sponge roller, a lower part of the roller is dipped in the developing liquid, whereas an upper part thereof is in rolling contact with the electrostatic latent image surface of the photosensitive drum. The developing liquid is absorbed into the sponge roller at its lower part, and the thus absorbed developing liquid is spread over the latent image surface.
In the above described contact type developing method, however, sufficient amount of developing liquid cannot be absorbed into the developer roller at its lower part due to the shortage in mass of the sponge. Further, since the developing liquid is absorbed into the roller while rotating the latter, sufficient amount of the developing liquid may not be transferred or supplied to the electrostatic latent image on the photosensitive drum. Accordingly, insufficient developing operation results, to thereby degrade a quality of a visible image.
Further, in the conventional contact type developing method, the developing roller is in always pressure contact with the photosensitive member an.d its retaining means, i.e, a photosensitive drum. Therefore, the developing roller and/or a unit for supporting the developing roller must be moved away from the photosensitive member and its retaining means, otherwise it becomes impossible to positively displace the developer roller, effect cleaning to the roller and to replace the roller by a new roller. To this effect, a special mechanism is required for moving the developing roller toward and away from the photosensitive member and the retaining means such as the photosensitive drum, which in turn, renders the overall device bulky and intricate.